I have a 1977 Mercury 1500 that blew from overheating.
I found a 85hp merc 4cyl Thunderbolt powerhead on craigslist. (http://cleveland.craigslist.org/boa/5008549813.html)
The owner said he's not sure of the Serial number, so I can't be sure of the year...
"Ok, I didn't find the serial # but I...